How can one trust that God will guide him?

Guidance is a grace from Allah and a divine bestowal upon whom He wills. The servant must strive for it by observing the obligatory duties, performing many supererogatory acts, and supplicating for steadfastness. He must attach his heart to Allah and rely upon Him. Reliance upon Allah for guidance is greater than reliance for sustenance. Whoever truly relies on Allah for his guidance will not be disappointed, in accordance with His (the Almighty's) saying: "And whoever relies upon Allah - then He is sufficient for him." The perfection of reliance is achieved by taking the necessary means while the heart is at peace with Allah. The perfection of reliance upon Allah for guidance is achieved by depending on Him and knowing that a person has no power or strength except through Him.